1. Field of the Invention
The present invention relates to an ink jet recording device and a bubble removing method.
2. Description of the Related Art
In an ink jet recording head mounted on the carriage of an ink jet recording device, a measure to image quality deficiency due to a bubble (ink droplet non-discharge) has been taken.
Image quality deficiency due to a bubble is caused in such a manner that a bubble larger than the cross-sectional size of an individual channel is attached to a portion for opening the edge of the individual channel in a common liquid chamber to clog the opening portion, resulting in inhibition of ink supply.
To remove the bubble, typically, an ink discharge opening is capped for negative-pressure suction so as to be discharged outside together with ink in the recording head.
Other than the ink discharge opening for printing, also typical is a method in which several to several tens of large dummy nozzles are provided to suction ink from the dummy nozzles, thereby suctioning and removing a bubble in the recording head.
To recover image quality deficiency due to a bubble produced in the recording head with respect to the related art, various proposals have been made. Some examples will be described hereinbelow.
Japanese Published Unexamined Patent Application No. Sho 63-224958 (hereinafter, referred to as related art 1) discloses that an elastic cap is pressed against an ink discharge opening to increase the internal pressure which is released into the atmosphere, and then, a suction recovery operation is performed.
Japanese Published Unexamined Patent Application No. Hei 2-78567 (hereinafter, referred to as related art 2) disclose that a pressurizing heater is provided aside from a recording heater, and the pressurizing heater can provide a dummy jet to reduce the ink consumption for discharge recovery, thereby shortening the recovering time.
Japanese Published Unexamined Patent Application No. Hei 4-219253 (hereinafter, referred to as a related art 3) discloses that a heater of an ink discharge opening adjacent to the ink discharge opening for discharge recovery is driven to discharge a bubble.
Japanese Published Unexamined Patent Application No. Hei 4-363253 (hereinafter, referred to as related art 4) discloses that in a recovery mode, an energy 1.48 times or more larger than a minimum energy which can form a bubble to perform ink discharge is supplied to perform preliminary discharge 1000 times or more.
Japanese Published Unexamined Patent Application No. Hei 5-155035 (hereinafter, referred to as related art 5) discloses that when a bubble is small and is diffused into ink within a predetermined time, printing is stopped corresponding to the diffusion time in ink.
Japanese Published Unexamined Patent Application No. Hei 7-195711 (hereinafter, referred to as related art 6) discloses that a bubble producing heater is provided aside from a recording heater, wherein a produced bubble and remaining bubbles are integrated to be suctioned reliably.
Japanese Published Unexamined Patent Application No. Hei 8-58095 (hereinafter, referred to as related art 7) discloses that an ink channel section between a recording head and an ink reservoir part is of a shape in which at least 90% of the entire length defines a circle having a diameter below 1 mm as a circumcircle so as to increase the flow velocity of the ink channel, thereby reliably removing a bubble when ink is suctioned.
Japanese Published Unexamined Patent Application No. Hei 8-169124 (hereinafter, referred to as related art 8) discloses that a discharge signal having a frequency higher than that of a discharge signal at recording is added at a recover operation, and then, suction is performed for recovery.
The following measures have been taken to the ink jet recording device in order to prevent nozzle clogging due to printing stop or permit recovery from clogging.
Japanese Published Unexamined Patent Application No. Sho 62-211150 (hereinafter, referred to as related art 9) discloses that pressurizing ink is supplied to an ink supply passage to flow the ink from a nozzle, thereby eliminating ink clogging and removing a bubble.
Japanese Published Unexamined Patent Application No. Sho 63-53047 (hereinafter, referred to as related art 10) discloses that a nozzle and a reciprocating pump are communicated to each other to perform a suction operation, thereby suctioning ink from the nozzle for a recovery operation.
Japanese Published Unexamined Patent Application No. Hei 5-229138 (hereinafter, referred to as related art 11) discloses an ink jet recording device using conductive ink, wherein when ink non-discharge is detected, the voltage of an ink discharge power source is increased to recover ink non-discharge.
Japanese Published Unexamined Patent Application No. Hei 7-186402 (hereinafter, referred to as related art 12) discloses that a nozzle part is brought into contact with a cap to be driven in a closed state so as to permit head temperature rise and recovery without wasting ink.
Japanese Published Unexamined Patent Application No. 2001-38925 (hereinafter, referred to as related art 13) discloses that a capping unit has a suction opening and a suction pump disposed in at least two spaced positions, allowing a closed valve to be in an open state while the upstream side valve of a recording head is opened and driving the suction pump selectively or simultaneously.
The related art for removing a bubble by negative-pressure suction including the related arts 1 and 6 to 8 has the following disadvantages.
Since the suction unit is necessary, the mechanism is complicated and the waste ink amount is increased.
To realize highly fine image quality such as a picture, a recording head for discharging a small amount of ink droplet is necessary. In such a recording head, the section of the ink discharge opening and the individual channel is a circle having a diameter of about several xcexcm to several tens of xcexcm or a rectangle having one side of about several xcexcm to several tens of xcexcm.
The cross-sectional area of the individual channel is reduced to increase the channel resistance. Unless the negative-pressure suction force is increased considerably, an ink flow velocity enough to suction and remove a bubble from the recording head cannot be obtained.
The related art for removing a bubble by the dummy nozzles has the following disadvantages.
The recording head is larger since the ink discharge opening not contributing to printing is formed. When the negative pressure in the recording head is high, a bubble is suctioned into the common liquid chamber from the ink discharge opening for the dummy nozzle with a large cross-sectional area.
The construction of the related art 2 has the disadvantage that the pressurizing heater is necessary so that the device is complicated.
In the construction of the related art 3, it is difficult to detect the ink discharge opening (individual channel) for discharge recovery, and more bubbles may be suctioned into the head from the ink discharge opening recovered by ink discharge from the adjacent ink discharge opening.
In the construction of the related art 4, since the heater is driven by an excessive energy as compared with ink discharge for normal printing, there arises the problem in the reliability of the electric circuit and the life of the heater.
In the construction of the related art 5, since printing is stopped together with bubble production, the printing processing ability is lowered.
The related art for preventing clogging has the following disadvantages.
In the construction of the related art 9, since the pressurizing unit is necessary, the device is larger and the device cost is increased. Ink can be leaked from the ink supply passage connection part by pressure at pressurization.
In the construction of the related art 10, a pump and solenoid are necessary for a suction operation. The device is larger and the device cost is increased.
In the construction of the related art 11, the power source cost is increased in order to vary the source voltage and there is a problem in reliability since clogging cannot be often eliminated though the voltage is increased.
In the construction of the related art 12, it is actually difficult to completely close all nozzles by a cap. Foreign particles attached to the cap member are attached to the nozzle. The cap is damaged by heat. There is a significant problem in reliability.
In the construction of the related art 13, plural suction pumps are necessary so that the device is larger and the device cost is increased. The waste ink amount not contributing to printing is large.
To eliminate the above disadvantages, the present invention provides an ink jet recording device and a bubble removing method which can prevent image deficiency by a simplified construction.
According to an aspect of the present invention, an ink jet recording device has: an ink jet recording head provided with a common liquid chamber to which ink is supplied from outside, individual channels communicated to the common liquid chamber each having an ink discharge opening formed in a front end thereof, and heating elements disposed in the individual channels discharging an ink droplet by heating ink; and a driving unit which applies a driving energy to the heating elements until ink present in the common liquid chamber is boiled.
A bubble produced in the common liquid chamber by a printing operation grows by the printing operation to clog the individual channel side edge of the common liquid chamber. Ink supply to the individual channel can be inhibited, resulting in possible image quality deficiency.
The driving unit drives the heating elements until a bubble is escaped from the common liquid chamber to the ink supply side. Ink in the common liquid chamber is boiled. The ink surface tension is lowered. The attaching force of the bubble to the wall surface is reduced. The bubble is expanded to increase the floating force. The bubble is spaced from the individual channel side edge of the common liquid chamber. The heating elements are used to boil ink so that the image quality deficiency can be recovered.
The driving unit may apply an ink discharging energy to the heating elements to continuously perform non-printing ink droplet discharge, thereby boiling ink.
In this case, the ink refill of the individual channel cannot cover the discharged ink due to the ink temperature rise. The ink meniscus position is backed to the common liquid chamber side edge of the individual channel.
As a result, the heating elements are driven in no ink state to increase the temperature. Ink in the common liquid chamber is boiled. The ink surface tension is lowered in the individual channel edge of the common liquid chamber. The bubble is expanded to increase the floating force. The bubble is spaced from the individual channel side edge of the common liquid chamber. The image quality deficiency can be recovered.
The driving unit may apply an energy smaller than the ink discharging energy for heating the recording head without discharging ink to the heating elements to boil ink.
In this case, no ink droplets are discharged from the ink discharge opening. In this state, the heating elements are driven until ink in the common liquid chamber is boiled. The ink surface tension is lowered due to the ink temperature rise. The attaching force of the bubble to the wall surface is reduced. The bubble is expanded to increase the floating force. The bubble is spaced from the individual channel side edge of the common liquid chamber. The image quality deficiency can be recovered. In addition, since ink discharge is not performed in order to boil ink, the waste ink amount by bubble removal can be reduced.
The ink jet recording device may further have a temperature detection unit which detects a temperature of the recording head. The temperature detection unit detects that the temperature of the recording head reaches a set boiling temperature, whereby the driving unit stops applying the driving energy to the heating elements. Ink in the common liquid chamber can be boiled reliably.
In this case, the set boiling temperature may be equal to or above an ink boiling point.
In general, when the temperature of the recording head is equal to or above the set boiling temperature, the ink temperature in the common liquid chamber in the recording head becomes equal to or above the boiling point to boil ink. The heating elements are driven until the temperature of the recording head reaches the set boiling temperature so as to remove a bubble clogging the individual channel side edge of the common liquid chamber.
The ink boiling point may be about 100xc2x0 C.
In the case of an aqueous ink, the boiling point is about 100xc2x0 C. The heating elements are driven until the temperature of the recording head reaches about 100xc2x0 C. Ink in the common liquid chamber can be boiled reliably. A bubble clogging the individual channel side edge of the common liquid chamber can be removed.
After detecting that the temperature of the recording head reaches the set boiling temperature, the temperature detection unit may detect that the temperature of the recording head is lowered to a set cooling temperature, whereby the driving unit applies an ink discharging energy to the heating elements to perform non-printing ink droplet discharge.
After ink is boiled, the ink is cooled to be thickened. When the decomposed (thickened) ink is present in the recording head, it leads to clogging and deterioration of printing performance. In the present invention, when ink in the common liquid chamber is boiled, an ink discharging energy is applied to the heating elements after cooling the ink to the set cooling temperature. Thereby the thickened ink is discharged to the outside. The set cooling temperature is a temperature at which the ink meniscus position moved to the common liquid chamber side by boiling returns to a predetermined position, that is, the temperature at which the ink can be discharged.
The set boiling temperature may be a temperature at which ink refill cannot cover the discharged ink and an ink meniscus position formed in the individual channel is formed on the common liquid chamber side rather than the heating element.
When the heating elements are used continuously, the ink refill cannot cover the discharged ink due to the ink temperature rise and the ink meniscus is moved to the common liquid chamber side edge of the individual channel. As a result, the high temperature ink reaches near the common liquid chamber side edge of the individual channel. A bubble attached to the individual channel side edge of the common liquid chamber can be removed.
A cross-sectional area of the common liquid chamber side edge of the individual channel may be smaller than that of a portion where the heating element is disposed.
When the driving unit drives the heating elements to discharge an ink droplet from the ink discharge opening, the cross-sectional area of the common liquid chamber side edge of the individual channel is larger than that of a portion where the heating element is disposed. The bubble point pressure is sufficiently high. When the ink meniscus is positioned at the common liquid chamber side edge of the individual channel, it is possible to prevent air from being suctioned into the common liquid chamber due to the negative pressure of the ink supply system.
The ink jet recording device may further have an ink supply chamber provided adjacent to the common liquid chamber in order to supply ink to the common liquid chamber having a volume in which an expanded bubble can be spaced from the common liquid chamber.
A bubble attached to the individual channel side edge of the common liquid chamber is expanded by the ink temperature rise and spaced from the edge. When the channel for supplying ink into the common liquid chamber is narrow, the expanded bubble can clog the channel to affect ink supply. The ink supply chamber provided adjacent to the common liquid chamber has a volume which can space the expanded bubble from the common liquid chamber. The bubble can be reliably spaced from the common liquid chamber so as to reduce the possibility to affect the ink supply.
The ink jet recording device may further have a detection unit which detects a number of printed sheets. When the number of printed sheets reaches a predetermined number of sheets, the driving unit drives the heating element, whereby a temperature of the recording head becomes equal to or above the set temperature.
In the common liquid chamber, the bubble is increased with printing. The temperature of the recording head becomes equal to or above the set boiling temperature for each predetermined number of sheets smaller than the number of printed sheets in which the bubble clogs the individual channel side edge of the common liquid chamber to cause image quality deficiency. The bubble is removed from the common liquid chamber to inhibit image quality deficiency.
The ink jet recording device may further have a detection unit which detects a number of accumulated discharges of ink droplets. When the number of accumulated discharges reaches a predetermined number, the driving unit drives the heating element, whereby a temperature of the recording head becomes equal to or above the set boiling temperature.
In the common liquid chamber, the bubble is increased with printing. The temperature of the recording head is becomes equal to or above the set boiling temperature for each predetermined number smaller than the number of accumulated discharges in which the bubble clogs the individual channel side edge of the common liquid chamber to cause image quality deficiency. The bubble is removed from the common liquid chamber to inhibit image quality deficiency.
The ink jet recording device may further have a head cleaning signal input unit which can input a head cleaning signal to the driving unit from outside. Based on the head cleaning signal inputted from the head cleaning signal input unit, the driving unit drives the heating elements, whereby a temperature of the recording head becomes equal to or above the set boiling temperature.
The user inputs a head cleaning signal from the head cleaning signal input unit to the driving unit. Then the temperature of the recording head becomes equal to or above the set boiling temperature to boil ink in the common liquid chamber. The bubble can be removed reliably.
According to another aspect of the present invention, an ink jet recording device has: a recording head having a common liquid chamber communicated with an outer ink source and with plural ink channels each having a heating element therein; and a driving unit for driving the heating element, wherein the driving unit applies an energy enough to boil an ink contained in the common liquid chamber near the ink channels.
The energy may be enough to discharge an ink in the ink channels.
Alternatively, the energy may not be enough to discharge an ink in the ink channels.
The ink jet recording device may further have: a temperature detector for detecting a temperature of the ink or recording head, wherein the driving unit primarily applies an energy to the heating elements, the energy not being enough to discharge the ink in the common ink chamber until the temperature detector detects a boiling temperature of the ink in the common chamber, and the driving unit secondarily applies an energy to the heating element, the energy being enough to discharge the ink in the common ink chamber after the temperature detector detects the temperature.
The driving unit may be controlled in accordance with an operator""s direction.
The ink jet recording device may further have a maintenance unit for maintaining the recording head by vacuuming an ink from the ink channels through an ink discharging portion.
The ink jet recording device may further have a control unit for independently controlling the maintenance unit and the driving unit for independent maintenance movement.
A method may be provided for removing an undesirable bubble formed between a common liquid chamber and ink channels each having a heating element therein in a recording head. The method has the steps of: applying an energy to the heating element until an ink near the ink channels in the common liquid chamber generates a bubble; merging the undesirable bubble and the generated bubble for forming a larger bubble having a relatively large buoyancy in the common liquid chamber; and removing the larger bubble through the common ink chamber due to the buoyancy.